Z01 HD 001123-11 LCE and Z01 HD 001124-11 LCE are companion projects that together investigate auditory communication in primates. The overall goal of these studies is to provide a comprehensive understanding of primate auditory communication in terms of development, neural mechanisms, endocrine factors, and social context. Two non-human primates, the squirrel monkey and common marmoset, are the main subjects of study, with additional data collected from other species where appropriate. Prior work in this project has shown that production of sounds that are the functional and acoustic equivalents of cry sounds in human infants are mediated by limbic cortex located along the anterior midline of the frontal lobe of the cerebral cortex, and that single neural elements in the auditory cortex (superior temporal gyrus) are particularly responsive to subtle differences in the acoustic structure of species-specific vocalizations, suggesting an important role in mediating individual differences (vocal signatures). Studies of endocrine mechanisms have shown that endogenous prolactin levels correlate with carrying time in infant retrieval tests, and that reducing prolactin by administering bromocryptine (a dopamine agonist) disrupts infant retrieval. New findings are (a) Squirrel monkeys engage in three types of affiliation: mothering, allo-mothering by other adult females, and same-sex affiliation among adult females. We are investigating cortisol, which is implicated in the stress response, and prolactin, which has been implicated in affiliative behavior with infants in other species. We hypothesize that prolactin will be associated with allo-mothering because of its clear role in lactation, and that it may be associated with same-sex adult friendships because it has also been implicated in affiliative behaviors that do not involve lactation, such as male parenting behavior. Preliminary results suggest that serum prolactin is positively associated with allo-mothering and with high levels of same-sex adult affiliation, and that serum cortisol is higher in animals with low overall rates of social interaction; b) a more refined analysis of a study on marmoset play behavior completed last year indicates that the majority of play time was spent with the same age playmate(s). Juveniles with older siblings played with siblings the most, and spent only 5.74 % and 1.40 % of the time playing with parents (father and mother, respectively). Juveniles housed without older siblings spent more time playing with parents (18.86 % and 15.50 %, father and mother, respectively). Morphine treatment (0.5 mg/kg subcutaneous injection in saline) significantly increased the duration of approach-withdraw play and frequency of all approach-withdraw elements except stalk. Frequencies of all elements of rough and tumble play were significantly increased by morphine administration. Play face also occurred more frequently after morphine administration (Ftreat, (4,67)df = 2.55, p< .05; p< .05), as did twittering, a vocalization used by young during play (Ftreat, (4,67)df = 2.87). The non-social play elements, toy manipulation (Ftreat, (4,27)df = 3.57, p< .05) and locomotor play (Ftreat (4,67)df= 6.59, p< .001; Ftreat, (4,67)df= 4.58,, p< .01), were significantly elevated under baseline conditions. Non-play social behaviors such as sitting with others (Ftreat,(4,34)df= 0.71, p> 0.05) and grooming (Ftreat, (4, 34)df= 1.09, p> 0.05), were unaffected by morphine. Overall, locomotor scores were significantly increased in the presence of morphine (Ftreat, (4,34)df = 18.61, p< .001).